These work so well because the systems are essentially springs which are highly constrained in all but the dimension intended for movement. Speaker drivers used as voice coil steppers operate similarly. The voice coil drivers sold for such purposes are not constrained, so a supporting structure is required. Speakers have these structures built-in and optimized for damping factor, so are ideal for this purpose. Most of the damping comes from the acoustics of the enclosure, but stand-alone drivers I've tested seem to be well enough damped without the enclosure to be useful for small-step stacking. I can't tell you how well an enclosure-less driver might work at high magnifications as I have not tested such a system, but up to 20-40x they seem ideal. At higher mags I do expect some sensitivity to room air movement, so there will be a limit to the step size for such a driver. Adding enclosure would greatly reduce this limit.

It's not clear to me what the ultimate limit is for step size in such a constrained system. I'd think it would be limited by the characteristics of the constraining springs. For a driver, there are two springs...the spider, and the surround. Someone much better at mechanics and materials than I might be able to tell you the limits, but I doubt there is any issue down to the nm range.

edited to add: another limit would be the noise level in the driving electronics. Not sure which wins (loses)...mechanical or electrical

I have a vintage (so to speak) pair of Yamaha NS-1000M speakers but that'a all I know about Beryllium. I wasn't aware of flexures until elf mentioned it. Dan's video series is excellent as well. Seems like I learn something new every day.

Last edited by Smokedaddy on Wed Mar 07, 2018 10:21 am; edited 1 time in total

These work so well because the systems are essentially springs which are highly constrained in all but the dimension intended for movement. Speaker drivers used as voice coil steppers operate similarly. The voice coil drivers sold for such purposes are not constrained, so a supporting structure is required. Speakers have these structures built-in and optimized for damping factor, so are ideal for this purpose. Most of the damping comes from the acoustics of the enclosure, but stand-alone drivers I've tested seem to be well enough damped without the enclosure to be useful for small-step stacking. I can't tell you how well an enclosure-less driver might work at high magnifications as I have not tested such a system, but up to 20-40x they seem ideal. At higher mags I do expect some sensitivity to room air movement, so there will be a limit to the step size for such a driver. Adding enclosure would greatly reduce this limit.

It's not clear to me what the ultimate limit is for step size in such a constrained system. I'd think it would be limited by the characteristics of the constraining springs. For a driver, there are two springs...the spider, and the surround. Someone much better at mechanics and materials than I might be able to tell you the limits, but I doubt there is any issue down to the nm range.

edited to add: another limit would be the noise level in the driving electronics. Not sure which wins (loses)...mechanical or electrical

Ray,

I would think with proper design the electrical noise could be made arbitrarily small since the bandwidth doesn't need to be high. A 1Hz or lower bandwidth seems reasonable for stacking, and a few nanovolt/rt(Hz) noise levels are possible. So environmental noise is probably the bigger noise source, and as you mentioned airflow is a major concern at these levels. I've even had to deal with airflow induced "noise" with ultra-precise electronics!

I would think with proper design the electrical noise could be made arbitrarily small since the bandwidth doesn't need to be high. A 1Hz or lower bandwidth seems reasonable for stacking, and a few nanovolt/rt(Hz) noise levels are possible. So environmental noise is probably the bigger noise source, and as you mentioned airflow is a major concern at these levels. I've even had to deal with airflow induced "noise" with ultra-precise electronics!

Best,

Sure, with appropriate filtering the electrical factors could be eliminated. As we know the gain is fairly low in such a system, on order of 1mm/V, or perhaps 3 orders of magnitude below where noise would impact.